Round-robin experiment in high-temperature gel permeation chromatography

The results of an interlaboratory or round-robin experiment in high-temperature gel permeation chromatography (HT-GPC) analysis are presented. The intention was to determine and raise awareness of interlaboratory reproducibility of HT-GPC techniques. Fifteen laboratories performed analyses of five polyethylene samples and standards SRM 1475 and 1476. Reproducibility, as measured by the interlaboratory standard deviation (s(LAB)), was greatly influenced by the breadth of the molecular weight distribution (MWD) and branching. The s(LAB), values for the weight-average molecular weight (M-w) of linear polyethylenes of narrow and broad MWDs were 4 and 14%, respectively. For branched polymers, GPC viscometry methods are shown to measure significantly higher molecular weights than the noncoupled GPC method, with higher variance. For branched polyethylenes measured with GPC viscometry, the reproducibility of M-w was characterized by s(LAB) = 18%. Reproducibility of the SRM 1475 standard was better than for unknowns. The results for branched standard SRM 1476 emphasize the important role of the detection method in GPC but call into question the use of this material as a molecular weight standard. For single-site polyethylene, only a handful of labs measured an MWD that closely matched the Flory distribution. Qualitatively, the responses indicate that many variations in instrument and analytical methods exist among laboratories; this is partly a reflection of the development and refinements that this technique must yet undergo before a truly standard method is widely accepted and practiced. (C) 2002 Wiley Periodicals, Inc.